Gilman titration

Butyllithium was purchased from EMC Corporation Lithium Division and its concentration was determined by double titration by the Gilman method.4... 

The alkyl methacrylate monomers were available from various sources. Isobutyl methacrylate (IBMA) (Rohm and Haas) and t-butyl methacrylate (TBMA) (Rohm Tech) may be purified first by distillation from CaH, followed by distillation from trialkyl aluminum reagents as described in detail earlier (20,21). In particular, t-butyl methacrylate (b.pt. 150°C) was successfully purified by distillation, from triethyl aluminum containing small amounts of diisobutyl aluminum hydride. The trialkyl aluminum and dialkyl aluminum hydride reagents were obtained from the Ethyl Corporation as 25 weight percent solutions in hexane. The initiator, -butyllithium, was obtained from the Lithco Division of FMC, and analyzed by the Gilman "double titration" (22). 

Butyllithium in hexane was purchased from E. Merck and titrated according to the method of Gilman.2 The checkers used recently purchased material from Aldrich Chemical Company, Inc., without titration. 

Butyllithium in pentane was purchased from Alfa Products, Morton/Thiokol Inc. and was titrated by the method of Gilman and Cartledge.23 The checkers used a 1.56 N hexane solution purchased from Mitsuwa Chemical Co. after titration by th Kofron-Baclawski procedure.215... 

Available from Ventron Corporation, Alfa Products, Beverly, MA 01915. t The molarity of the butyllithium solution may be checked before use by the procedure devised by Gilman.3 This involves careful hydrolysis of a measured sample using excess distilled water, followed by titration against standard hydrochloric acid solution with phenolphthalein as indicator. Since the butyllithium solution may contain some lithium hydroxide, it is necessary to carry out an identical titration of a sample which has undergone complete reaction with benzyl chloride in order to determine the lithium hydroxide present. From the difference between the two titrations, the molarity of the butyllithium may be calculated. 

Scheme 9.17). The macrocycle (A) of Scheme 9.1 is the dpp-incorporating 30-membered ring 8 used earlier for making catenanes (see Protocol 5) it is sufficiently small to prevent release of the bis-porphyrin dumbbell. The preparation of 22+ takes place in seven steps.1819 One of the starting materials is 4-lithiotoluene 13, which may be obtained by direct interaction of an excess of freshly cut lithium with 4-bromotoluene 12 in ether under argon at reflux (Scheme 9.10).12 The resulting organolithium compound is titrated by the double titration method described by Gilman et alP The experimental procedure is very similar to that described in Protocol 1.

Butyllithium was freshly titrated by the method of Gilman.2 Excess strong base, either butyllithium or lithium diisopropylamide (LDA), (exceeding 1 equiv per diphenylacetonitrile) should be avoided since the resulting Thorpe-Ziegler cyclization product is susceptible to fragmentation under the reaction conditions to afford 1,1-dicyano-4,4-diphenylbutane. 

Such exchange reactions between mercurials and lithium alkyls and between mercurials and Grignard reagents had previously been demonstrated by Gilman and Jones 49> as well as by Salinger and Dessy 105>. In addition, Daniel and Paetsch 39> carried out a low temperature oxidation of the ylid with molecular oxygen in tetrahydrofuran, producing a soluble peroxide whose presence was detected both by iodometric titration with sodium thiosulfate and by the isolation of formaldehyde from the reaction mixture after hydrolysis of the formocholine intermediate 3 with acid. 

All solubilities at room temperature (22°C) analysis using Gilman double titration (17) b Slurry present—only solution in equilibrium was analyzed. 

Analysis of solutions using Gilman double titration with a time period of about three weeks (17)... 

The yield for the 26-mole Run 10, Table IV, was determined by GLC (using the trimethylsilyl derivative) and by the Gilman double titration technique, both of which gave 100% yield (17). The product solution was clear, dark red-brown, and had good thermal stability. The concentrated solutions were highly reactive to air but did not ignite. (The solution should be stored cool or frozen when stored for longer than four months.)... 

Gilman double titration does not give good results with this amine yield based ... 

Thermal Stability of Organolithium—TMEDA Complexes. About 400 ml of the organolithium-TMEDA complex was placed in a bottle and then analyzed using the Gilman double titration (17). The bottle was placed in a circulating constant-temperature oil bath at the desired temperature (usually 35°C) and left for 30 days. The solution was reanalyzed. 

Determination of the concentration of Grignard reagents is often important for their further preparative use and is best effected by titration with acid as elaborated by Gilman s school 112... 

Gilman titration220 gives the total alkali (organolithium + alkoxide) when one aliquot is titrated first with water and then with standardized HCl. Quenching a second aliquot with benzyl chloride and followed by titration with H2O and then standardized HCl gives the alkoxide concentration. The difference in these values is the molarity of the organolithium. 1,3-Diphenylacetone tosylhydrazone (189).221 2,5-dimethoxybenzyl... 

Leonhardt et al had observed that vinyl lithium gave low recoveries in the Gilman and Haubein double titration procedure and this, coupled with the observation that their samples contained small amounts of lithium acetylide as an impurity, prompted them to look for an alternate specific gas chromatographic method of assay for vinyl lithium. Their method is described below. 

Titrate n-butyllithium using the Gilman double quench procedure before use (1 mL quenched with... 

Titrate n-butyliithium using the Gilman double quench procedure before use (1 mL quenched with 1,2-dibromoethane and 1 mL with water, each titrated with 1 M HCI using methyl orange indicator. Subtraction gives true alkyiiithium concentration). 

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